The only two shuttles left in active service is the Atlantis, and the Endeavour. The Endeavour made her first flight May 7, 1992. The Atlantis, on the other hand, made her first flight October 3, 1985, So she is significantly older then the Endeavour. The Enterprise was retired and is now at the Hazy center, just outside Washington D.C., and the Columbia and Challenger were lost. So out of six, two remain in service, the youngest two of the fleet. Below is a breakdown of the shuttle fleet:

Enterprise; Built in 1977, she never actually flew in space.

Columbia; First flight was April 12, 1981. She spent over 300 days in space. She was lost February 1, 2003, when she broke up on re-entry.

Challenger; First flight was April 4, 1983. She spent just over 62 days in space. She was lost January 28, 1986, at just three years old, during the launch process.

Discovery; First flight was August 30, 1984. She spent over a year in space all together. She retired today after 27 years of service.

Atlantis; First flight was October 3, 1985. She has spent over 293 days in space thus far. She is slated at this time to make the final shuttle flight this summer.

Endeavour; First flight was May 7, 1992. She has spent over 280 days in space thus far. The youngest ship in the fleet, she is slated to make the second to last shuttle flight this spring.

it's good to see all went well with this flight, in the statement after landing he said that not a single system failure occurred, so they can use the instruments as spare parts.

I would have expected that the crew went around, instead of returning to earth. They could have taken the courage to park this shuttle on the moon and be hero's for ever as the first men (and woman) on the moon, since no one else ever been there...

Pretty much any vehicle or vessel is usually considered to be female. It goes back a long way in history to the days when ships were the ideal mode of transportation. Traditionally, most ships were named after, or in honor of a female. Commonly the wife/daughter/mother of the boats owner or captain, or a female in power (I.E. Queen Mary, Queen Elizabeth).

"Steady as she goes!"

"The searchers all say they'd have made Whitefish Bay had they put fifteen more miles behind her." Lyrics from Grodon Lightfoot, about a ship with a male name, the "Edmund Fitzgerald".

...all the way up to "I'm givin' it all she's got, Captain!" (Add heavy Scottish accent, if you like... )

Below are just a few examples of famous ships with female names:

#1: Steamer "Empress Of Britain"

#2: Steamer "Queen Mary"

#3: Lake Freighter "Courtney Burton", sister ship to the "Edmound Fitzgerald". Oddly enough, most lake ships are given male names, or named after landmarks or cities along the lakes. Few actually have female names, but all are called "her".

#4: Fishing Vessel "Andrea Gail", lost in the Atlantic during "The Perfect Storm" (yes, that's a true story).

World War Two saw a lot of aircraft with female names or references to females..."Shoo Shoo Shoo Baby", "Lady Luck", "Pretty Polly", "Playmate", "Diamond Lil", "D-Day Doll", "Slick Chick", and "Blonde Bomber" to name a few. Most of the nose art that went along with those names is not appropriate to post here, but below are a few examples of nose art and names that are appropriate to post.

#1: Probably the most famous one, B-17F "Memphis Belle".

#2: This beautiful bird resides at KYIP, owned by the "Yankee Air Force", B-17G "Yankee Lady".

#3: B-17G "Sentimental Journey" is owned by the "Commemorative Air Force".

#4: B-25J "Show Me", owned by "Commemorative Air Force".

I hope this helps...I know it's a long answer to a short question...but in a very round-about way, that is why the space shuttle is called "her".